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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2023
Dec. 31, 2022
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Unconsolidated variable interest $ 72 $ 68
Cash Surrender Value of Life Insurance 254 246
Corporate owned life insurance, borrowings 110 110
Ameren Illinois Company    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Cash Surrender Value of Life Insurance 120 118
Corporate owned life insurance, borrowings 110 $ 110
Partnership Funding Commitment    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Outstanding funding commitments $ 17